JTree aufklappen

import java.util.ArrayList;

import javax.swing.BoxLayout;

import javax.swing.JFrame;

import javax.swing.JPanel;

import javax.swing.JScrollPane;

import javax.swing.JTree;

import javax.swing.SwingUtilities;

import javax.swing.tree.DefaultMutableTreeNode;

import javax.swing.tree.DefaultTreeModel;

import javax.swing.tree.MutableTreeNode;

public class TreeTest {

  JFrame frame;

  JTree tree;

  DefaultTreeModel model;

  MutableTreeNode root;

  public void show() {

    frame = new JFrame("Tree Test");

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JPanel panel = new JPanel();

    panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));

    tree = new JTree();

    panel.add(new JScrollPane(tree));

    DefaultTreeModel model = (DefaultTreeModel)tree.getModel();

    tree = new JTree(model);

    ArrayList<DefaultMutableTreeNode> node_list = new ArrayList<DefaultMutableTreeNode>(50);

    node_list.add(new DefaultMutableTreeNode("a1"));

    node_list.add(new DefaultMutableTreeNode("a2"));

    node_list.add(new DefaultMutableTreeNode("a3"));

    node_list.get(0).add(node_list.get(1));        // a2 an a1 hängen

    node_list.get(1).add(node_list.get(2));        // a3 an a2 hängen

    model.setRoot(node_list.get(0));

    tree.expandRow(1);

    tree.expandRow(2);

    frame.setContentPane(panel);

    frame.setSize(400,400);

    SwingUtilities.invokeLater(new Runnable() {

      public void run() {

        frame.setVisible(true);

      }

    });

  }

  public static void main(String[] a) {

    TreeTest t = new TreeTest();

    t.show();

  }

}